Experimental evaluation of the transient and steady state performance of an air-cooled square minichannel heat exchanger

Abstract

Transient and steady state performance of an air-cooled square minichannel heat exchanger was experimentally evaluated. 82 minichannels of square cross section, 11 cm long and 2 mm width, were manufactured on AISI 316 L. Heat sinks made of aluminium were attached to each side of the heat exchanger. Natural and forced air convection were investigated, while the hot fluid was flowing in the downward counterflow direction. Two other variables were changed: inlet water temperature, from 34.8 to 75.4 °C, and water flow rate, from 5.7 to 29.1 kg/h, while in the case of forced air convection its velocity was fixed at 0.75 m/s. Ambient air temperature and water temperature and pressure at the inlet and outlet were measured. Results obtained include the thermal resistances and heat capacities in the different parts of the heat exchanger, the transient time, the residence time of water inside the heat exchanger and the time constant of the device. Correlations were obtained to predict the duration of the transient period in the natural and forced convection cases. Additionally, a lumped mass heat transfer model was developed to estimate the time evolution of the average water temperature in the heat exchanger.